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FreeBSD-SA-22:05.bhyve                                      Security Advisory
                                                          The FreeBSD Project

Topic:          Bhyve e82545 device emulation out-of-bounds write

Category:       core
Module:         bhyve
Announced:      2022-04-06
Credits:        Mehdi Talbi, Synacktiv
Affects:        All supported versions of FreeBSD.
Corrected:      2022-04-05 22:59:52 UTC (stable/13, 13.1-STABLE)
                2022-04-06 01:56:57 UTC (releng/13.1, 13.1-RC1-p1)
                2022-04-06 03:04:14 UTC (releng/13.0, 13.0-RELEASE-p11)
                2022-04-05 23:03:35 UTC (stable/12, 12.3-STABLE)
                2022-04-06 03:06:28 UTC (releng/12.3, 12.3-RELEASE-p5)
CVE Name:       CVE-2022-23087

For general information regarding FreeBSD Security Advisories,
including descriptions of the fields above, security branches, and the
following sections, please visit <URL:https://security.FreeBSD.org/>.

I.   Background

bhyve(8) is a hypervisor that supports running a variety of guest
operating systems in virtual machines.  It implements a number of device
models, including an emulated Intel 82545 network interface adapter.

II.  Problem Description

The e1000 network adapters permit a variety of modifications to an Ethernet
packet when it is being transmitted.  These include the insertion of IP and
TCP checksums, insertion of an Ethernet VLAN header, and TCP segmentation
offload ("TSO").  The e1000 device model uses an on-stack buffer to generate
the modified packet header when simulating these modifications on transmitted
packets.

When checksum offload is requested for a transmitted packet, the e1000 device
model used a guest-provided value to specify the checksum offset in the on-
stack buffer.  The offset was not validated for certain packet types.

III. Impact

A misbehaving bhyve guest could overwrite memory in the bhyve process on the
host, possibly leading to code execution in the host context.

The bhyve process runs in a Capsicum sandbox, which (depending on the FreeBSD
version and bhyve configuration) limits the impact of exploiting this issue.

IV.  Workaround

Only the e1000 device model is affected; the virtio-net device is not
affected by this issue.  If supported by the guest operating system,
presenting only the virtio-net device to the guest is a suitable workaround.
No workaround is available if the e1000 device model is required.

V.   Solution

Upgrade your vulnerable system to a supported FreeBSD stable or
release / security branch (releng) dated after the correction date,
and restart bhyve virtual machines.

Perform one of the following:

1) To update your vulnerable system via a binary patch:

Systems running a RELEASE version of FreeBSD on the amd64, i386 platforms can
be updated via the freebsd-update(8) utility:

# freebsd-update fetch
# freebsd-update install

2) To update your vulnerable system via a source code patch:

The following patches have been verified to apply to the applicable
FreeBSD release branches.

a) Download the relevant patch from the location below, and verify the
detached PGP signature using your PGP utility.

# fetch https://security.FreeBSD.org/patches/SA-22:05/bhyve.patch
# fetch https://security.FreeBSD.org/patches/SA-22:05/bhyve.patch.asc
# gpg --verify bhyve.patch.asc

b) Apply the patch.  Execute the following commands as root:

# cd /usr/src
# patch < /path/to/patch

c) Recompile the operating system using buildworld and installworld as
described in <URL:https://www.FreeBSD.org/handbook/makeworld.html>.

Restart the applicable bhyve virtual machines, or reboot the system.

VI.  Correction details

This issue is corrected by the corresponding Git commit hash or Subversion
revision number in the following stable and release branches:

Branch/path                             Hash                     Revision
- -------------------------------------------------------------------------
stable/13/                              53f722094798    stable/13-n250272
releng/13.1/                            5a28d8befda0  releng/13.1-n250078
releng/13.0/                            b85c68857da3  releng/13.0-n244795
stable/12/                                                        r371867
releng/12.3/                                                      r371871
- -------------------------------------------------------------------------

For FreeBSD 13 and later:

Run the following command to see which files were modified by a
particular commit:

# git show --stat <commit hash>

Or visit the following URL, replacing NNNNNN with the hash:

<URL:https://cgit.freebsd.org/src/commit/?id=NNNNNN>

To determine the commit count in a working tree (for comparison against
nNNNNNN in the table above), run:

# git rev-list --count --first-parent HEAD

For FreeBSD 12 and earlier:

Run the following command to see which files were modified by a particular
revision, replacing NNNNNN with the revision number:

# svn diff -cNNNNNN --summarize svn://svn.freebsd.org/base

Or visit the following URL, replacing NNNNNN with the revision number:

<URL:https://svnweb.freebsd.org/base?view=revision&revision=NNNNNN>

VII. References

<URL:https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2022-23087>

The latest revision of this advisory is available at
<URL:https://security.FreeBSD.org/advisories/FreeBSD-SA-22:05.bhyve.asc>
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